/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.resolver;

import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.FutureListener;
import io.netty.util.internal.UnstableApi;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.io.Closeable;
import java.net.SocketAddress;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;

/**
 * Creates and manages {@link NameResolver}s so that each {@link EventExecutor} has its own resolver
 * instance.
 */
@UnstableApi
public abstract class AddressResolverGroup<T extends SocketAddress> implements Closeable {

  private static final InternalLogger logger = InternalLoggerFactory
      .getInstance(AddressResolverGroup.class);

  /**
   * Note that we do not use a {@link ConcurrentMap} here because it is usually expensive to
   * instantiate a resolver.
   */
  private final Map<EventExecutor, AddressResolver<T>> resolvers =
      new IdentityHashMap<EventExecutor, AddressResolver<T>>();

  protected AddressResolverGroup() {
  }

  /**
   * Returns the {@link AddressResolver} associated with the specified {@link EventExecutor}. If
   * there's no associated resolved found, this method creates and returns a new resolver instance
   * created by {@link #newResolver(EventExecutor)} so that the new resolver is reused on another
   * {@link #getResolver(EventExecutor)} call with the same {@link EventExecutor}.
   */
  public AddressResolver<T> getResolver(final EventExecutor executor) {
    if (executor == null) {
      throw new NullPointerException("executor");
    }

    if (executor.isShuttingDown()) {
      throw new IllegalStateException("executor not accepting a task");
    }

    AddressResolver<T> r;
    synchronized (resolvers) {
      r = resolvers.get(executor);
      if (r == null) {
        final AddressResolver<T> newResolver;
        try {
          newResolver = newResolver(executor);
        } catch (Exception e) {
          throw new IllegalStateException("failed to create a new resolver", e);
        }

        resolvers.put(executor, newResolver);
        executor.terminationFuture().addListener(new FutureListener<Object>() {
          @Override
          public void operationComplete(Future<Object> future) throws Exception {
            synchronized (resolvers) {
              resolvers.remove(executor);
            }
            newResolver.close();
          }
        });

        r = newResolver;
      }
    }

    return r;
  }

  /**
   * Invoked by {@link #getResolver(EventExecutor)} to create a new {@link AddressResolver}.
   */
  protected abstract AddressResolver<T> newResolver(EventExecutor executor) throws Exception;

  /**
   * Closes all {@link NameResolver}s created by this group.
   */
  @Override
  @SuppressWarnings({"unchecked", "SuspiciousToArrayCall"})
  public void close() {
    final AddressResolver<T>[] rArray;
    synchronized (resolvers) {
      rArray = (AddressResolver<T>[]) resolvers.values().toArray(new AddressResolver[0]);
      resolvers.clear();
    }

    for (AddressResolver<T> r : rArray) {
      try {
        r.close();
      } catch (Throwable t) {
        logger.warn("Failed to close a resolver:", t);
      }
    }
  }
}
